As illustrated in FIGS. 10 and 11, a known combustion burner 80 to be mounted to a boiler furnace includes air-supply nozzles 84, 86 for supplying combustion air disposed on an outer periphery of a fuel-supply nozzle 82 for supplying fuel. Such a combustion burner 80 is often equipped with a swirler 88 disposed in an air supply passage, for securing swirl flame-holding performance.
The swirler 88 normally swirls combustion air and supplies the combustion air to a combustion space 100 of the boiler furnace, and forms a swirl flow 92 of air which a flow of fuel injected from the fuel-supply nozzle 82 in the combustion space 100 is made the center. The swirl flow 92 of air rapidly expands with a distance from the combustion burner 80, due to a centrifugal force. Thus, an inverse pressure gradient with a pressure decreasing toward the center is generated in the swirl flow 92. This inverse pressure gradient forms a flow flowing toward the center of the swirl flow 92 at a position of the swirl flow 92 away from the combustion burner 80 by a certain distance. Accordingly, combusted gas is circulated, and the high temperature of the combusted gas ignites non-combusted air-fuel mixture (fuel+air) to hold a flame.
For instance, JPH8-61609A discloses a liquid-fuel burner including an air supply passage for supplying primary air, disposed on an outer periphery of an oil-spraying nozzle, and a swirler for swirling the primary air, disposed on a distal end portion of the air supply passage.
Further, though not equipped with a swirler, JP2008-510618A (translation of a PCT application) discloses a nozzle assembly including an air-supply passage disposed on an outer periphery of a liquid-supply nozzle for supplying a liquid flow. This nozzle assembly is configured to atomize a liquid supplied by the liquid-supply nozzle and to inject the atomized liquid. In addition, the nozzle assembly is equipped with a crash pin to promote breakage of atomized liquid particles, thereby functioning to prevent accumulation of liquid around a bottom section of the crash pin.